On Dec 19, 2007 1:06 AM, John Vogel
You do realize that the example you gave is just as general as all the tutorials.
Here is an example I was working, but it gives a segmentation fault for some reason:
example.h
typedef struct { unsigned char a; unsigned char b; unsigned char c; unsigned char d; } IP;
IP* shiftIP(IP* addr);
example.c
#include "example.h"
IP* shiftIP(IP* addr){ unsigned char t; t = addr->a; addr->a = addr->b; addr->b = addr->c; addr->c = addr->d; addr->d = t; }
return addr; ? or rather, void shiftIP.
Example.hsc
{-# OPTIONS -ffi -fglasgow-exts #-} module Example where
import Foreign import Foreign.C.Types import Control.Monad
#include "buzz.h"
data MyIP = MyIP { a :: CUChar , b :: CUChar , c :: CUChar , d :: CUChar } deriving (Show)
instance Storable MyIP where sizeOf _ = #{size IP} -- 4 alignment _ = alignment (undefined :: CUChar) -- 1 peek p = return MyIP `ap` (#{peek IP, a} p) `ap` (#{peek IP, b} p) `ap` (#{peek IP, c} p) `ap` (#{peek IP, d} p) poke p ip = do #{poke IP, a} p $ a ip #{poke IP, b} p $ b ip #{poke IP, c} p $ c ip #{poke IP, d} p $ d ip
foreign import ccall safe "static buzzlib.h shiftIP" shiftIP :: Ptr MyIP -> Ptr MyIP
shiftIP isn't a pure function. shiftIP :: Ptr MyIP -> IO (Ptr MyIP) or shiftIP :: Ptr MyIP -> IO ()
shiftMyIP :: MyIP -> MyIP shiftMyIP ip = unsafePerformIO . alloca $ \ptr -> poke ptr ip >> peek (shiftIP ptr)
shiftMyIP ip = unsafePerformIO . alloca $ \ptr -> poke ptr ip >> peek =<< (shiftIP ptr) or shiftMyIP ip = unsafePerformIO . alloca $ \ptr -> poke ptr ip >> shiftIP ptr >> peek ptr -- Cheers, Lemmih